Dissolution Of Silicate Rocks Research Articles

Major Ion Chemistry of Surface Water and Its Controlling Factors in Ebinur Lake Basin

The sustainable development of arid regions is significantly constrained by the availability of water resources, which play a crucial role in this context. It is necessary to deeply investigate and analyze the hydrochemical characteristics and major ion sources. This study, which was based on data from 183 water samples collected from the Jinghe River Basin, provided a comprehensive analysis of the river water hydrochemistry. The results show that the average TDSs (total dissolved solids) was measured at 49.8 mg·L−1. HCO3− (82.4%) and Ca2+ (77.1%) were the ions present in the highest abundances. The river water was classified as the HCO3−-Ca2+ hydrochemical type. The Gibbs diagrams indicated that the ion composition was primarily influenced by rock weathering. Additionally, the Na-normalized molar ratio diagrams suggested that the chemical composition was primarily governed by the weathering and dissolution of silicate rocks, while the carbonate rock dissolution played a lesser role. This study demonstrates a critical aspect of water resources quality evaluation, which is of great significance for the sustainable development, utilization and environmental protection of regional water resources.

An Analytical Method for Quantification of Sn Isotope Variations in Geological Materials Using MC‐ICP‐MS

A robust analytical method is presented here, for measurements of Sn isotope variations with high precision using a multi‐collector inductively coupled plasma‐mass spectrometer (MC‐ICP‐MS). A silicate rock dissolution procedure was used, together with means to remove organic matter introduced by the resin during ion‐exchange chromatography. The two‐stage ion exchange chromatography efficiently isolates Sn from the matrix and isobarically interfering elements, from samples with variable Sn mass fractions (~ 0.03 to 7 μg g−1). A double spike technique was also implemented to correct any secondary mass bias induced during sample processing and isotope ratio measurements. An intermediate precision (2s) of ± 0.47 was obtained for ε122/118Sn (using internal normalisation; n = 70 over a period of 29 months), ± 0.021‰ for δ122/118Sn (using double spike; n = 176 over a period of 29 months) and ± 0.059‰ for δ122/118Sn (using Sb doping; n = 34 over a period of 4.5 months) for the Sn standard solution, NIST SRM 3161a (Lot# 140917). The δ122/118SnNIST SRM 3161a of eleven geological reference materials are reported for the first time (BIR‐1a, BRP‐1, DTS‐2b, ECRM 782‐1, JP‐1, OKUM, QLO‐1a, RGM‐2, SGR‐1b, STM‐2 and UB‐N), with five others (AGV‐2, BCR‐2, BHVO‐2, GSP‐2 and W‐2a) showing similar results to previous studies, generally with improved precision. The intermediate precision (2s) of replicate dissolutions of ten RMs (AGV‐2, BCR‐2, BHVO‐2, BIR‐1a, DTS‐2b, GSP‐2, OKUM, SGR‐1b, STM‐2 and W‐2a) varied from 0.003 to 0.054‰. Typical repeatability precision (2SE) of individual measurements of these ten RMs over multiple measurement sessions varied from 0.031 to 0.297‰ (with 120Sn+ beam intensity < 2.37 V) and 0.017 to 0.025‰ (with 120Sn+ beam intensity > 2.37 V).

Multi-method characterization of groundwater nitrate and sulfate contamination by karst mines in southwest China

Groundwater contamination by nitrate and sulfate in mining areas is a significant challenge. Consequently, the inputs sources of these contaminants and their evolution have received considerable attention, with the knowledge gained critical for improved management of water quality. This study integrated data on multiple stable isotopes and water chemistry data and a Bayesian isotope mixing model to investigate the relative contributions of inputs sources of sulfate and nitrate sources to bodies of water in a karst mining area in southwest China. The outcomes indicated that hydrochemical component in the water bodies of the study area is mainly derived from the dissolution of silicate rocks, carbonate rocks and sulfate minerals as well as the oxidation of sulfides. The human and agricultural wastewater, soil nitrogen, and fertilizers were the predominant inputs sources of nitrate to the mine water environment; the predominant inputs sources of sulfide were mineral oxidation, evaporite dissolution, atmospheric deposition, and sewage. Groundwater is mainly recharged from atmospheric precipitation, and surface water is closely hydraulically connected to groundwater. Nitrogen and oxygen isotope composition and water chemistry indicative of nitrification dominate the nitrogen cycle in the study area. The oxidation of pyrite and bacterial sulfate reduction (SRB) had no significant impact on the stable isotopes of groundwater. The results of this study demonstrate the inputs of different sources to nitrate and sulfate in karst mines and associated transformation processes. The results of this study can assist in the conservation of groundwater quality in mining areas and can act as a reference for future related studies.

Hydrogeochemical process and coal mining-motivated effect on the hydrochemistry for the groundwater system in mining area of Western China

The Jurassic coalfield in the mining area of western China exhibits a multi-layered groundwater system. However, it is subject to an arid and semi-arid climate with limited water resources. Consequently, the ecological environment is highly vulnerable, and the chemistry and quality of groundwater may be influenced by multiple factors. This study systematically the coal mining-motivated effect on the hydrochemistry and water quality of the groundwater system, using the Caojiatan Coal Mine as a case study. The analysis incorporates a combination of the self-organizing maps (SOM), entropy-weighted water quality index (EWQI), and traditional hydrochemical analysis methods. After coal mining, there was an increase in the proportion of HCO3-Ca and HCO3-Mg in the groundwater samples of J2z, J2y4, and J2y5. The groundwater is controlled by cation exchange as a whole. The J2y4 and above groundwater is influenced by both the dissolution of carbonate and silicate rocks before coal mining. After coal mining, the Quaternary and J2a groundwater in the western wing is primarily influenced by the dissolution of carbonate rocks; the J2z, J2y4 and J2y5 groundwater is primarily governed by the dissolution of silicate rocks and the oxidation of FeS2; the J2y3 and below groundwater is primarily controlled by the dissolution of evaporate rocks. The resulting dilution effect after coal mining and the implementation of measures for the discharge of treated mine water make the groundwater quality of the J2y4 and higher aquifers tend to be better. The research findings serve as a valuable reference for promoting the sustainable development and protection of groundwater resources not only in the study area but also in other coal mines.

Hydrologic and Landscape Controls on Rock Weathering Along a Glacial Gradient in South Central Alaska, USA

AbstractRock weathering impacts atmospheric CO2 levels with silicate rock dissolution removing CO2, and carbonate dissolution, pyrite oxidation, and organic rock carbon oxidation producing CO2. Glacierization impacts the hydrology and geomorphology of catchments and glacier retreat due to warming can increase runoff and initiate landscape succession. To investigate the impact of these changes on catchment scale weathering CO2 balances, we report monthly samples of solute chemistry and continuous discharge records for a sequence of glacierized watersheds draining into Kachemak Bay, Alaska. We partition solute and acid sources and estimate inorganic weathering CO2 balances using an inverse geochemical mixing model. Furthermore, we investigated how solutes vary with discharge conditions utilizing a concentration‐runoff framework. We develop an analogous fraction‐runoff framework which allows us to investigate changes in weathering contributions at different flows. Fraction‐runoff relationships suggest kinetic limitations on all reactions in glacierized catchments, and only silicate weathering in less glacierized catchments. Using forest cover as a proxy for landscape age and stability, multiple linear regression shows that faster reactions (pyrite oxidation) contribute less to the solute load with increasing forest cover, whereas silicate weathering (slow reaction kinetics) contributes more. Overall, in glacierized catchments, we find elevated weathering fluxes at high runoff despite significant dilution effects. This makes flux estimates that account for dilution more important in glacierized catchments. Our findings quantify how glaciers modify the inorganic weathering CO2 balance of catchments through hydrologic and geomorphic forcings, and support the previous hypothesis that deglaciation will be accompanied by a shift in inorganic weathering CO2 balances.

Reservoirs and Hydrogeochemical Characterizations of the Yanggao Geothermal Field in Shanxi Province, China

Geothermal water is the product of deep circulation within the crust, and the understanding of its hydrogeochemical process can provide effective information for integrated research on its circulation pattern and formation mechanism. Based on the geothermal geological conditions of the Yanggao geothermal field, this study analyzed water samples from thermal springs and geothermal wells in the geothermal field, ascertaining their hydrochemical components, along with their hydrogen and oxygen isotopes. Using methods like piper diagrams, ionic component ratio characterization, Na–K–Mg equilibrium diagrams, and reverse path simulations, this study elucidated the recharge source of geothermal water in the study area, revealed the water–rock interactions the geothermal water experienced, and evaluated the geothermal reservoir temperatures. The results show that the geothermal water has hydrochemical types of Na–Cl–HCO3 and Na–HCO3–Cl, and is primarily recharged by the atmospheric precipitation in the northern mountainous area. The geothermal water has experienced extended water runoff and deep thermal circulation, and its hydrochemical composition primarily results from the weathering and dissolution of silicate rocks and evaporites. The major hydrogeochemical processes of the geothermal water involve the dissolution of calcite, dolomite, gypsum, and kaolinite. In addition, the canon-exchange also changes the chemical component of the geothermal water. The SiO2 Geothermometer, a multimineral equilibrium diagram, and the silica–enthalpy model reveal the presence of deep and shallow geothermal reservoirs in the study area, which exhibit temperatures of 73 °C and ranging from 125 to 150 °C, respectively. The open geothermal reservoir environment results in the mixing of geothermal water and cold water, with shallow and deep geothermal water mixing with cold water at ratios of 57% and 76%, respectively.

Formation processes of groundwater in a non-ferrous metal mining city of China: Insights from hydrochemical and strontium isotope analyses.

Tongling is a significant non-ferrous metal mining city in China, which produces waste that negatively impacts the area's water environment. It is essential to comprehend the hydrochemical properties and formation processes of groundwater to safeguard and utilize it efficiently. We explored major ions, strontium, and its isotopes in water and river-bottom samples from the northern (i.e., A-A' section) and southern (i.e., B-B' section) areas. The hydrochemical facies show the mining activities have a greater impact on surface water than on groundwater. Groundwater hydrochemical formation results from several factors, with water-rock interaction and ion exchange being primary. Additionally, the dissolution of calcite, dolomite, and feldspar, oxidation of pyrite, and hydrolysis of carbonate minerals also impact the formation of groundwater chemistry. Our analysis of strontium and its isotopes indicates that carbonate dissolution primarily occurred in the recharge area; the runoff from the recharge to the discharge area results in the dissolution of certain silicate rocks; calcite dissolution sources account for > 70% contribution in both surface water and groundwater water-rock interactions, whereas silicate rock dissolution sources and dolomite dissolution sources account for < 30%. Due to changed order of dissolved carbonate and silicate minerals during groundwater flow, the distribution of strontium and its isotopes in the A-A' section is opposite to that in the B-B' section. The findings provide a basis for developing, utilizing, managing, and protecting groundwater resources, especially in similar mining areas.

Contrasting sources and enrichment mechanisms in lithium-rich salt lakes: A Li-H-O isotopic and geochemical study from northern Tibetan Plateau

Lithium (Li), a crucial mineral resource for modern high-tech industries, is notably abundant in the northern Tibetan Plateau, primarily within lithium-rich salt lakes. However, the exploration and development of these resources are hindered due to an incomplete understanding of their nature and origin. Here we present results from a comprehensive study on the hydrochemical parameters, whole-rock geochemistry, H-O isotopes, and Li concentrations in surface brine, river water, geothermal springs, and associated rocks from two representative lithium-enriched salt lakes, the Laguo Co (LGC) and Cangmu Co (CMC) in Tibet to understand the genetic mechanisms. Our water-salt balance calculations and H-O isotopic analysis reveal that Li in LGC and CMC primarily originates from the Suomei Zangbo (SMZB, ∼91%) and Donglong Zangbo (DLZB, ∼75%) rivers, respectively. It is estimated that the LGC and CMC took a minimum of 6.0 ka and 3.0 ka to accumulate their current lithium resources, respectively. The distinct geological characteristics reflect evolutionary differences between the two lakes, suggesting diverse lithium sources and enrichment processes. The high lithium ion concentration and light lithium isotope composition in the SMZB river waters indicate the genetic relationship with lithium-enriched geothermal springs in the Tibetan Plateau. Our results suggest that lithium in the LGC originates from lithium-enriched geothermal springs and is primarily supplied through the small-scale SMZB river. In contrast, the formation and evolution of CMC are influenced by the northern Lunggar rifts, receiving a prolonged and stable input from the DLZB, resulting in high lithium concentrations and isotopic values. The absence of lithium-enriched geothermal springs and the prevalence of silicate rocks in the CMC catchment suggest that lithium may be sourced from the weathering of silicate rocks, such as granitic pegmatite veins containing lithium-rich beryl, widely distributed in the upstream area of DLZB. The forward modeling approach, quantifying the contribution fractions of different reservoirs (atmospheric precipitation, silicate, carbonate, and evaporite), indicates that the distinct lithium concentrations in the mainstream (>1 mg/L) and tributaries (<0.1 mg/L) are positively correlated with the ratio of silicate contributions to carbonate contributions, suggesting that dissolved lithium in river waters primarily originates from the weathering and dissolution of silicate rocks. The distinct sources and enrichment mechanisms of lithium in these two salt lakes are attributed to various evolutionary processes, topographical features, hydrological factors, fundamental geological settings, and tectonic histories, despite their spatial proximity. Furthermore, our study highlights the significant role of rivers in the formation of young salt lakes, in addition to geothermal springs.

Groundwater chemistry and isotope for interpreting the hydrogeological conditions and hydrochemical evolution of multilayer aquifer system of Donghai island, China

Groundwater is generally important water resource for islands. Groundwater recharge source and its hydrochemical characteristics are vital issues for the sustainable development and management of island groundwater resources. In this study, taking Donghai island which is featured with multi-layer aquifer structure as an example, by comprehensive using of statistical analysis, stable isotope (2H-18O), Gibbs diagram and ion ratio graph, we conducted a comprehensive hydrochemistry investigation for the groundwater in the shallow aquifer (i.e., phreatic and feeble confined aquifers) and middle confined aquifer of this island. And the hydrochemical characteristics, recharge sources, hydrogeochemical processes and source of element components of groundwater in different aquifers of Donghai island were identified. The results show that the major ions and TDS of the shallow groundwater are higher than those of the confined groundwater, and that those aquifers have not suffered significant seawater intrusion. The main hydrochemical types of shallow groundwater and confined groundwater are Cl·SO4-Ca·Na and HCO3-Na·Mg, respectively. Different hydrochemical types and chemical component concentrations between these two aquifers indicate that the hydraulic relationship between aquifers is relatively weak. The results of 2H-18O stable isotope and deuterium excess indicate that the shallow groundwater originated from local precipitation and that the recharge period of the confined groundwater is different from the shallow groundwater. Results of ion ratio reveal that the island groundwater hydrochemistry is mainly controlled by the water-rock interaction, featuring with dissolution of silicate rocks (such as sodium feldspar, potassium feldspar, calcium feldspar and biotite). In addition, cation exchange is also an important hydrogeochemical process controlling the hydrochemical composition of the confined groundwater. The results will be helpful for understanding of the local island hydrogeology and be supportive for the groundwater resources quantitative research such as numerical modeling for Donghai island.

Origin and hydrogeochemical formation processes of geothermal fluids from the Kibiro area, Western Uganda

The Kibiro geothermal field, located in the western branch of the East African Rift Valley System, has many geothermal surface manifestations. Several geochemical research has already been carried out in this area. However, the sources of dissolved ions in geothermal fluids have not been assessed so far. The hydrochemical and gas isotopic characteristics have been examined in this study to identify and determine the sources of the main dissolved components and the geochemical processes involved in the formation of the geothermal fluid. Methods applied in the analysis of the genesis and hydrogeochemical evolution of geothermal fluids include isotope tracers, major ion ratios, graphical methods (stability diagrams, durov diagrams, chloro-alkaline indices, piper diagrams, and HNC-plot), and hydrogeochemical simulations using PHREEQC software. The Kibiro hot springs are high salinity Na–Cl waters. Based on δ18O and δ2H values, the geothermal waters are found to be of meteoric origin. The assessments indicate that Na+ and Cl− are derived from halite dissolution. The dissolution of dolomite, calcite, gypsum, and anhydrite is responsible for the concentration of Ca2+, Mg2+, SO42−, and HCO3−. The main source of K+ is derived from the dissolution of silicate rocks (K-feldspar). The gas isotopes analysis indicates that 97.5% of He with isotope ratio of 0.217 Ra mainly originates from crustal sources and 2.47% is derived from the mantle. 51.39% of CO2 originates from marine limestone, 46.55% from sedimentary organic carbon and 2.06% from the mantle. This evidence further confirms that there are no direct inputs of volatiles from a magma chamber below the Kibiro geothermal field. The evolution of the fluids suggests that most of the common cations and anions found in the Kibiro hot spring waters originated from high-temperature water/rock interaction.

Hydrochemical Characteristics and Groundwater Quality Assessment Using an Integrated Approach of the PCA, SOM, and Fuzzy c-Means Clustering: A Case Study in the Northern Sichuan Basin

Groundwater is a precious resource that is vital for human life. Widespread human activities occur in the Sichuan basin due to befitting climate and geological conditions, inducing a series of groundwater contamination. In this article, hydrochemical analysis, principal component analysis (PCA), self-organizing map (SOM), and fuzzy c-means clustering (FCM) were integrated to reveal the hydrochemical process and assess groundwater quality in the northern part of the Sichuan Basin based on a collection of 203 groundwater samples. The groundwater hydrochemical types were dominated by the HCO3-Ca type. The PCA results show both natural and anthropogenic factors contributed to the hydrochemical compositions. The combination of the SOM and FCM classifies neurons into two categories: the first category where NO2− and NH4+ are most similar, perhaps as anthropogenic sources of pollution, which pose serious threats to human health; and the second category, where the total dissolved solids, Ca2+, Na+, Cl−, SO42, Mg2+, and K+ are most similar, explained as the influence of natural factors. The ion source was determined by water–rock interactions: Na+ mainly comes from the dissolution of silicate rocks, while Ca2+, Mg2+, and HCO3− from the dissolution of calcite and dolomite. Cation exchange was recognized in the water–rock interactions. The achievements would provide a significant reference for groundwater protection in the Sichuan Basin.

Genome and transcriptome analysis of rock-dissolving Pseudomonas sp. NLX-4 strain

Microbial weathering processes can significantly promote soil properties and reduce rock-to-soil ratio. Some soil-inhabiting bacteria exhibit efficient rock-dissolution abilities by releasing organic acids and other chemical elements from the silicate rocks. However, our understanding of the molecular mechanisms involved during bacterial rock-dissolution is still limited. In this study, we performed silicate rock-dissolution experiments on a Pseudomonas sp. NLX-4 strain isolated from an over-exploited mining site. The results revealed that Pseudomonas sp. NLX-4 strain efficiently accelerates the dissolution of silicate rocks by secreting amino acids, exopolysaccharides, and organic acids. Through employing genome and transcriptome sequencing (RNA-seq), we identified the major regulatory genes. Specifically, 15 differentially expressed genes (DEGs) encoding for siderophore transport, EPS and amino acids synthesis, organic acids metabolism, and bacterial resistance to adverse environmental conditions were highly up-regulated in silicate rock cultures of NLX-4 strain. Our study reports a potential bacterial based approach for improving the ecological restoration of over-exploited rock mining sites.Graphical

Deciphering the signatures of weathering and erosion processes and the effects of river management on Li isotopes in the subtropical Pearl River basin

Lithium (Li) isotopes signatures in sedimentary archives are promising proxies to reconstruct paleo-weathering rates and paleo-seawater composition. Nonetheless, the interpretation of the seawater Li isotope composition evolution over the Cenozoic is still debated. In this aim, the study of large rivers can provide constraints for continental weathering flux to the ocean. However, in the recent past, human activities like flow regulation via reservoir construction, have significantly modified the hydrodynamic of riverine systems, impacting the transfer of matter from the continent to the ocean. Hence, these effects need to be considered and investigated when unravelling the signature of natural processes from river borne materials.We report Li concentrations and Li isotope compositions (δ7Li) for the dissolved and sediment loads of subtropical river waters from the Xijiang basin, the largest tributary of the Pearl River (also known as the Zhujiang), Southern China. These rivers display low dissolved Li concentrations. Although they are potentially impacted by carbonate dissolution in the upstream karst terrains, the Li budget of these rivers is dominated by silicate weathering. The dissolved Li isotope compositions of rivers vary over a range from +16‰ to +27‰. These values are high compared to the estimated composition of the bedrock (~0‰), and are explained by the preferential incorporation of the light 6Li in solid weathering products formed during the incongruent dissolution of silicate rocks. We show that the variations of the dissolved δ7Li values across the basin reflect changes in silicate weathering intensity which controls the formation of secondary phases. The high δ7Li values in the headwaters reflect greater degree of secondary phase formations associated with the higher erosion rates in the mountainous part of the basin, whereas the lower δ7Li values in the lowlands characterized by low soil erosion rates and more abundant rainfall reflect a more intensive weathering. This interpretation is supported by the positive relationship between soil erosion rates and the Li dissolved fluxes. The isotope compositions of the suspended particulate material (SPM) transported by rivers in the Xijiang Basin (from −3.8‰ to −0.7‰) are systematically lower than the composition of the bedrock. We observe that the δ7Li of most SPM samples collected during the wet season are lower than those of samples collected during the dry season. We interpret this seasonality as a consequence of seasonal changes in the sediment properties due to water regulation. In spite of the influence induced by river managements on the river sediments, our data also highlight that the imprint of weathering and erosion processes is still preserved in the sedimentary load of the Xijiang as suggested by the relationship between the SPM δ7Li values and the weathering intensity defined as the ratio between the chemical weathering rates and the total denudation rates. Altogether, our study confirms the robustness of Li isotopes as a proxy of weathering and erosion processes, even in this heavily-managed river system.

Lithium and potassium isotope fractionation during silicate rock dissolution: An experimental approach

This study experimentally investigates the isotopic behaviors of Li and K during the dissolution of silicate rocks (i.e., basalt and granite). Proton-driven dissolution (in 0.8 M HNO3) and ligand-driven dissolution (in 5 mM critic acid or oxalic acid) experiments were performed in batch-closed systems over 15 days. We provide a time-series interpretation of Li and K isotope fractionation during silicate dissolution in ultra-acidic (unidirectional) and near-natural (biologically affected) environments. As the reaction progressed, we measured large isotope fractionation between the liquid (l) phase and the pristine silicate (s) phase, ranging from −10.3 to 0.1‰ (Δ7Lil-s) and from −1.01 to −0.11‰ (Δ41Kl-s) through the early stage of dissolution (<24 h). The enrichment of lighter Li and K isotopes in the solutions rapidly diminished as rock dissolution continued and gradually approached equilibrium to the end of experiments. In contrast, resorption of pre-leached isotopically lighter Li on silicate residuals during ligand-driven dissolution produced lighter isotope enrichment in the solutions compared to the initial rock by up to 2.8‰. Despite the preferential dissolution of specific minerals, the isotope fractionation patterns of Li and K do not vary with lithology, indicating limited inter-mineral isotopic differences. During the experiments, the Li and K isotopic pattern could be divided into two-to-three stages. The initial enrichment of light isotopes in the liquids can be ascribed to the kinetic isotope effect, confounded by diffusion and ion solvation. A later transition towards no isotope fractionation of Li and K may be explained by (i) the masking effect from dissolution, and (ii) an imprint from the destruction of 7Li/41K-enriched surface layers. Lateral resorption of solute Li after ~100 h reaction could be facilitated by the electrostatic attraction from increasing surface negative charges and active hydroxyls with increasing pH during ligand-driven dissolution (pH ~ 4) relative to proton-driven dissolution (pH ~ 0.2). Therefore, the presence of organic ligands impacts dissolution stoichiometry, and potentially modifies Li isotope fractionation in natural weathering environments. In comparison, K isotope fractionation driven by rock dissolution stops immediately (within days) after starting the experiments. This research helps to understand the mechanisms of Li and K isotope fractionation during chemical weathering and trace long-term climate change using geological records.

Lithium and potassium isotope fractionation during silicate rock dissolution: An experimental approach

Lithium and potassium isotope fractionation during silicate rock dissolution: An experimental approach

Chemical Characteristics of Groundwater and Material Sources Analysis in Shiqi River Basin

To investigate the chemical characteristics of groundwater and material sources in a typical karst hill (valley) depression, 41 groundwater samples were systematically collected in the Shiqi River basin. The statistical analysis of the conventional ion content in the groundwater shows that pH of the groundwater in the study area is between 6.06-8.07, the total solid solubility is between 18.21 mg ·L-1 and 336.28 mg ·L-1, and the charges of anions and cations in the water body are balanced. Ca2+, Mg2+, and HCO3- are the main ions in groundwater, with concentrations of 2.61-108.7 mg ·L-1, 0.54-27.61 mg ·L-1, and 8.1-370.74 mg ·L-1, respectively. The groundwater characteristics in the study area are consistent with the high calcium and weak alkalinity characteristics of karst water. By using the Gibbs diagram, piper diagram, end-member analysis, and ion proportional coefficient, hydrochemical characteristics and material sources of groundwater were further analyzed. The results show that Ca2+ and Mg2+ are mainly controlled by the weathering of limestone and dolomite in which carbonic acid is involved. Na+ mainly comes from the dissolution of silicate rocks. At the same time, Ca2+ and Na+ undergo cationic exchange adsorption in the groundwater flow process. K+, Cl-, and NO3- are mainly affected by agricultural fertilizer application and domestic wastewater discharge. The hydrogen and oxygen isotope analysis of groundwater shows that atmospheric precipitation is the main recharge source of groundwater in this region, which impacts the chemical characteristics and material sources of local groundwater. The results of this study show that the geological background of groundwater is the main factor that affects its hydrochemical characteristics and material sources in areas with relatively little anthropogenic activity.

Multistep sequestration and storage of CO2 to form valuable products using forsterite

The potential use of mineralogical carbonation is greatly acknowledged not only in reducing CO2 emissions through carbon capture and storage (CCS) but also in producing industrially viable products. The direct carbonation of stable silicate minerals by supercritical CO2 is unrealistic due to the low conversion efficiencies. The natural abundance of silicate minerals (e.g., olivine) is theoretically sufficient to fix the entire quantity of man-made CO2 emissions, while carbonation of sorbents obtained from the dissolution of silicate rocks could proceed in a multistep (or continuous) process. In this work, the optimum experimental conditions for a multistep procedure of sequestration of minerals and conversion of CO2 into valuable products were investigated using synthetic forsterite. In this research, magnesium sulfate obtained from the dissolution of forsterite in aqueous H2SO4 was successfully carbonated to produce valuable byproducts (e.g., silica and hydrates of magnesite) with an economical carbonation as a means of CO2 mitigation. Hydromagnesite, while being commercially applied in various fields (e.g., fire retardation and catalysis), can be transformed to magnesite which is stable for millions of years.

Inorganic carbon flux and its source in the karst catchment of Maocun, Guilin, China

New findings have shown that the contribution of carbonate weathering to the atmospheric CO2 sink is far greater than previous estimates, through the combined action of carbonate dissolution, the global water cycle, and photosynthetic uptake of dissolved inorganic carbon (DIC). However, in order for calculations to be accurate, any carbon source effect should be deducted from the overall carbon sink. In this study, we carried out high temporal resolution monitoring of flow and hydrochemistry within the Xiaolongbei (XLB) silicate catchment and Beidiping (BDP) carbonate catchment for 1 year. We found the dissolved inorganic carbon concentrations to be higher in BDP than in XLB, and the annual inorganic carbon fluxes in BDP are roughly 23.8 times higher than those in XLB. Similarly, the rate of carbonate rock dissolution is much higher than the rate of silicate rock dissolution. We find carbonate rock dissolution to respond rapidly to rainfall events, and it is sensitive to rainfall changes on hourly, diurnal, and seasonal scales. The high rate of carbonate rock dissolution gives rise to the high concentrations of DIC, Ca, Mg, and to the high inorganic carbon flux in this basin. Differences between the theoretical and calculated contributions of atmospheric and soil CO2 to the DIC are possibly due to CO2 outgassing.

Silicate rock dissolution by ammonium bisulphate for pH swing mineral CO2 sequestration

A wide range of mineral resources and different technical approaches can be employed to permanently sequester the CO2 into stable carbonates through mineral carbonation. The aim of this work was to investigate the dissolution and carbonation of olivine, pyroxene and amphibole-rich rocks using an ammonium salt pH swing mineral carbonation process. The effect of temperature (50, 70 and 100°C) and time (5, 10, 15, 30, 60, 120, 180min) and the dissolution kinetics were studied using a batch reactor at ambient pressure. Temperature had a direct effect on the rates of mineral dissolution reactions. The higher dissolution efficiency using olivine with particles 75–150μm was 77% in 3h at 100°C, with a limitation due to product layer diffusion with apparent activation energy of 31kJmol−1. The final CO2 sequestration efficiency using olivine was 70wt.%. Besides, only about 30% of Mg was extracted from pyroxene and amphibole at 100°C due to polymerisation of non-dissolved silica and deposition of sulphate minerals on their surface. Therefore, amphibole and pyroxene-rich rocks do not represent a resource for this process. Ammonia-based mineral carbonation could integrate geological storage where the last is not feasible and where CO2 emitters and olivine resources are closely co-located.

Deep source CO 2 in natural waters and its role in extensive tufa deposition in the Huanglong Ravines, Sichuan, China

The aqueous geochemistry of Huanglong Ravine, Sichuan, China, where tufa is being deposited extensively, is discussed using chemical composition data together with the carbon and oxygen stable isotope ratios. The water quality of tufa-depositing surface streams in this area is basically controlled by the mixing of two source waters—fault-bounded spring water and snow and/or glacier melt water. The spring water contains high concentrations of CO 2 supplied via faults: the resulting high concentration of dissolved CO 2 gives rise to much greater dissolution of carbonate rocks than is usual in karst springs and also to the dissolution of silicate rocks. Upstream spring waters in the Ravine are close to equilibrium with respect to calcite. Concentrations of dissolved inorganic carbon (DIC) and their δ 13C values result from the interaction of about 0.02 mol l −1 CO 2(aq) of δ 13C −3‰ with carbonate rocks of δ 13C +3‰ under closed system conditions. About 70% of the CO 2 is estimated to be supplied from the upper mantle. The data for all the springs fall in the kaolinite stability field, in agreement with observed dissolutional aggressiveness towards Na- and Ca-feldspar, and that the dissolution rates of these minerals are too slow to move the composition of these waters into the feldspar stability field. The DIC species in the surface streams are in isotopic equilibrium; variations in δ 13C DIC found at different sites are mainly due to differences in the degree of CO 2 degassing from the water. There is a linear relationship between δ 18O values and the altitude at which samples were collected; the oxygen isotope composition of surface stream water in this area is controlled by evaporation. Water chemistry in daytime and nighttime and daily change of pH in the surface water flowing on the tufa deposition indicate that biological activities contribute to the carbonate precipitation, although their extent is not great. The daily precipitation rate in this area is estimated to be 4300 kg as CaCO 3 day −1 over a surface area of 0.9 km 2, i.e, 0.1 cm year −1.